Hello guys, I have a transmission fault I'm trying to diagnose. Only Error code is p0741

Truck is a 2005 LR3 SE 4.4 v8, 192k miles (I've owned it since 145k). 6 spd ZF transmission.

The fault started this summer. First it was towing the boat uphill only. When accelerating to maintain speed, The transmissio fault message would pop up and The rpms would jump up. Then in the fall it started doing it when towing and accelerating.

Now it does it anytime we accelerate onto the freeway or going uphill. if we take it easy on acceleration then it won't come on until the truck has been at freeway speed for about 10 seconds.

I figured the trans was due for a service so the pan / filter was replaced and 6 quarts of new zf lifeguard fluid was pumped in recently.

It did not change the fault frequency or circumstances of when the fault pops up at all. Same as before after the service.

Truck was shifting and driving great before the trans service and still shifts and accelerates great. No other noticeable behaviors other than the fault itself.

alternator is putting out 14.5v and the battery is 2 months old. Truck gets about 15 mpg in mixed city highway driving.

Im trying to nail down the cause of this fault.

Any help or guidance would be greatly appreciated!

thank you

- Phil

 

LR-P0741.jpg

That is a Torque Converter Slip code, which means the computer is trying to apply the converter, but based on input vs output speed sensors, it is detecting that it isn't engaging. It "could" be an issue with the Mechatronics (aka valvebody + TCM) but is usually the Torque Converter itself (turbine shaft seal inside failes, or the converter clutch fails).

 

So I paid close attention to when the fault popped up on the drive to work this morning and as long as I stayed below 70mph, the fault did not appear and the torque converter clutch was locked in and functioning normally.

As soon as I went above 70mph in top gear, it triggered immediately and bumped up the rpms 400.

Could this be a wheel speed sensor issue even though there is no code for that?

 

No, probably still a converter issue. You likely are putting enough load on the converter clutch in order to maintain 70 MPH that the converter can't stay locked in. I can't say for sure that it IS the converter just based on what has been discussed, but I bet it is a good possibility.

I doubt a Wheel Speed sensor malfunction would cause this. The P0741 fault is indicating there is slippage inside the transmission detected. Its comparing the input speed sensor and output speed sensor, both located inside the transmission. It narrows it down to the converter based on what is applied and the amount of slippage detected.

 

Thank you for the information.

Will it hurt the vehicle to continue to drive with the converter lock not staying on?

could it be a failing solenoid issue and not the tc clutch itself?

 

Im not a trans guru, but have dealt with a couple hand fulls of failed LR3 transmissions.

I have been told that that code is caused by worn bushings in the trans. Not sure if you can bench test a TC, but it would suck to pull the trans, replace the TC just to find its more than that.

LRtechniker obviously has more savoir faire in this matter, but I couldn't resist chiming in.

In my opinion driving a vehicle with a slipping trans will cause more damage regardless of the root cause.